In general, a radio frequency identification (RFID) system utilizes RFID tag devices that are either attached to, or integrally formed in, objects that are to be identified or otherwise tracked for various types of applications. In addition, an RFID reader device (alternatively referred to as an “interrogator device”) is utilized to communicate with an RFID tag device using a signaling scheme. With conventional signaling schemes, communication between an RFID reader and an RFID tag is commonly implemented using radio signals, wherein both the RFID reader and the RFID tag include separate receive and transmit antennas and associated transmitter and receiver circuitry. In such signaling schemes, transmission and receiving of signals can occur concurrently, wherein different RF frequencies are used for the transmit and receive modes of operation. In addition, such conventional signaling schemes must implement complex, area-consuming circuitry such as PLLs (phase-locked loops) and VCOs (voltage-controlled oscillators) to generate clock signals for controlling clocking functions on circuitry of the RFID tag device. Moreover, some RF tag devices have a battery, which can be an active battery, or a battery that is activated when in the presence of an RFID reader.
As industry standards continue to demand smaller footprint RFID tags for specialized applications (e.g., RFID tags with an integration area less than 100 μm×100 μm), it becomes problematic and non-trivial to construct RFID tags with conventional frameworks. For example, the use of two integrated antenna systems on a RFID tag device for receive and transmit modes requires a significant amount of real estate. While RFID tag devices can be implemented to operate at higher frequencies (e.g. 2.5 GHz) with smaller on-chip antennas, such antennas can still be relatively large and area consuming, and thus, not practical for very small footprint RFID tag devices. Moreover, when integration area is limited, mutual coupling and interference can occur between the transmit and receive antennas on the RFID tag device. Furthermore, as RFID tag decrease in size, it becomes impractical to use batteries or complex, area consuming power generating circuitry.